Identification of Potential Grapevine Red Blotch Virus Vector in Missouri Vineyards

Grapevine red blotch virus (GRBV), the causal agent of grapevine red blotch disease, has been detected in vineyards across the United States and throughout Missouri. Insect transmission of GRBV in cultivated vineyards of Missouri has not been investigated previously. The objectives of this study were to characterize the potential insect vectors present in four commercial vineyards that had previously been determined to be infected with GRBV, test potential vectors caught in vineyards and surrounding habitats for the presence of GRBV with the use of PCR, and investigate the ability of candidate vectors to acquire and transmit GRBV using controlled greenhouse experiments. Of the vineyard-collected insects tested over the course of this research, one species of treehopper, Entylia carinata, tested positive for GRBV. This species and one other treehopper, Enchenopa binotata, were selected for direct transmission assays. Both species successfully acquired GRBV from infected grapevines and transmitted GRBV to confirmed GRBV-free grapevines. E. carinata has been identified as a promising economic vector after insect samples from vineyards tested positive for GRBV, and monitoring data placed this species as the second-most abundant treehopper captured in traps. We do not consider E. binotata a likely economically significant vector because our monitoring data showed that this species was rare and only found along edge habitat surrounding vineyards, never inside vineyard rows. Samples of the most abundant treehopper, Micrutalis calva, have not tested positive, but its vector status remains unresolved. Further research on rates of secondary spread and transmission by M. calva are required, but these results provide evidence that insect transmission of GRBV is feasible in the region.